Introduction - Seafish · Web viewTo test the two designs, it was necessary to observe the fish that escaped through the T90 sections and compare with the fish that were retained

Fisheries Science Partnership 2015/16

Developing the selective Net Grid trawl in the English North East Nephrops trawl fishery

Fisheries Science Partnership: FSP (2015-16) (47)

Authors: Frank Armstrong, Patrick Jones & Joanna Ford, Tom CatchpoleIssue date: June 2016

A DEFRA supported project

Cefas Document Control

Title: Developing the selective Net Grid trawl in the English

North East Nephrops trawl fishery

Submitted to: Harry Sampson - Defra

Date submitted: 16 June

Project Manager: Frank Armstrong

Report compiled by: Frank Armstrong

Quality control by: Tom Catchpole

Approved by & date: Tom Catchpole

Version: 2

Version Control History

Author Date Comment Version

Frank Armstrong 10/04/2016 First draft Draft 1

Tom Catchpole 10/06/2016 Edits, analysis,

conclusions

Draft 2

Further Trials of the Net Grid Page i

Executive Summary

This work was carried out as part of the Fisheries Science Partnership (FSP) programme. The trawler Luc SN 36 was chartered for 14 days between October and December 2015 to undertake trials in the Nephrops fishery off the North east coast of England. The specific objective was to modify the incline panel and the escape hole of the selective Net Grid trawl design to enable retention of marketable fish while still minimising catches of unwanted fish. The Net Grid is made of a 4-panel box section inserted into a standard two-panel trawl into which an inclined sheet of netting is laced. On top of the box section in front of netting grid is a fish escape hole. The netting grid acts as a physical barrier and guides fish out of the escape-hole while Nephrops pass through the netting to the cod end.

Prior to this project, Cefas in collaboration with several kippers from the NE English Nephrops fishery, had shown it was possible to catch Nephrops with very low cod catches using the Net Grid trawl (the initial motivation for the design), however, this also meant large reductions in the catches of other marketable fish. Therefore, while the Net Grid was efficient at minimising fish catches while retaining Nephrops, it was considered a rather blunt tool, whereby skippers could either catch fish (including unwanted fish) and Nephrops with a conventional trawl or only Nephrops with the Net Grid trawl. The idea came from the industry to further develop the Net Grid design so that it could retain marketable fish while still avoiding unwanted catches.

The modifications to the Net Grid were to the escape hole at the top of the inclined netting grid in order to retain large marketable fish, and to the length of the inclined netting grid so that there was space at the bottom of the grid under which marketable fish could pass. Two modifications were tested, a simple cover of the escape hole with T90 120mm netting and the insertion of a larger section of T90 120mm in the top of the trawl above the netting grid including the area of the escape hole. Both designs included removing 8 meshes from the bottom edge of the inclined netting grid.

To test the two designs, it was necessary to observe the fish that escaped through the T90 sections and compare with the fish that were retained in the cod end of the trawl. This was done by designing a cover over the T90 escape sections which terminated in a secondary top (cover) cod end. The catches retained in the two cod ends demonstrated which fish had entered the trawl and escaped through the T90 sections compared with those which were retained in the trawl and would have been caught if the trawl was applied commercially.

In both trials, most whiting (70%) and haddock (58-75%) were caught in the top cod end and therefore would have alluded capture with these designs. These species are known to move to the top of the trawl during the capture process and were small enough to pass through the 120mm meshes of the T90 sections. Flat fish species, including plaice, lemon sole, sole, dab and brill were caught in the bottom cod end along with species of ray. Cod were mostly caught in the bottom cod end (70-85%) and therefore would be mostly retained with a commercial application if this design.

These modifications to the Net Grid trawl show it is possible to maintain catches of flatfish, rays and most cod, while avoiding most haddock and whiting and other unwanted catches. Whiting has been identified as the species posing the highest risk to fishing businesses in the transition to the discard ban in this fishery so there is useful application for this design. These latest variants of the Net Grid, while retaining marketable catches also retain more unwanted catches that previous versions, also, earlier variants which avoid almost all marketable catches are still the only design available to avoid cod while targeting Nephrops. However, these designs do provide more options to skippers who are motivated to change the selectivity of their trawls so that their catches composition matches more closely with quota composition and so assist them in the transition to the landing obligation.

Further Trials of the Net Grid Page ii

Table of contents

1 Introduction.............................................................................................................................. 1

1.1 The Fisheries Science Partnership..........................................................................................1

1.2 Background............................................................................................................................1

1.3 Objective................................................................................................................................2

2 Material and Methods..............................................................................................................3

2.1 Vessel.....................................................................................................................................3

2.2 Gear.......................................................................................................................................3

2.3 Area and period of survey......................................................................................................7

2.3.1 Scoping Study...............................................................................................................................................7

2.3.2 Survey..........................................................................................................................................................7

2.4 Experimental Design..............................................................................................................8

2.5 Sampling Plan........................................................................................................................8

3 Results.................................................................................................................................... 11

3.1 Catch composition...............................................................................................................11

3.2 Percentage of catches separated between the cod end and cover.....................................12

3.3 Trial 1 retained and discarded in bottom (commercial) cod end.........................................13

3.4 Trial 1 retained and discarded in top (cover) cod end.........................................................13

3.5 Trial 2 retained and discarded in bottom (commercial) cod end.........................................14

3.6 Trial 2 retained and discarded in top (cover) cod end.........................................................14

3.7 Trial 1 effect of modifications on length of fish caught........................................................15

3.8 Trial 2 effect of modifications on length of fish caught........................................................17

4 Discussion.............................................................................................................................. 19

5 Conclusions........................................................................................................................... 20

6 References.............................................................................................................................. 21

7 Acknowledgements...............................................................................................................21

8 Annexes.................................................................................................................................. 22

Further Trials of the Net Grid Page iii

1 Introduction

1.1 The Fisheries Science Partnership

The Fisheries Science Partnership (FSP) is a Defra-funded collaborative research programme of scientific research between the UK fishing industry and scientists. Since it was established in 2003 the programme has undertaken around 100 projects, covering annual time-series surveys of stocks subject to traditional assessments and ad hoc projects on, e.g., gear selectivity, discard survival, tagging and migration, and fishery development. A full description of the aims and all completed reports of the FSP programme can be found on the Cefas website (www.cefas.defra.gov.uk). Charter of suitable fishing vessels for projects approved by Defra and its FSP steering committee is arranged through an open tendering procedure and scientific and operational work plans are developed in line with the agreed and commissioned project, between Cefas and the selected vessel.

Fishing gear selectivity has featured highly in the FSP programme and both scientists and industry continue to seek ways of improving gear design to minimise discarding. As with previous FSP projects, this work investigates the selectivity of demersal trawls by exploring design features that take advantage of behavioural trends of fish species.

1.2 Background

The new Common Fisheries Policy Regulation (European Parliament and Council Reg. No.1380/2013) establishes a phased introduction of a landing obligation (also known as the discard ban) under which the catch of any fish species that are subject to catch limits must be landed and counted against quotas of each Member State. The landing obligation started on 1 January 2015 for pelagic fisheries, and introduces other fisheries through to 1 January 2019. Its introduction is one of the most significant reform elements in the new CFP, and represents a fundamental shift in the management approach to EU fisheries.

Article 15(11) of the new CFP basic Regulation, which deals with the landing obligation, states that the use of fish below specified sizes is restricted to uses other than direct human consumption, for example fish meal. The expectation is that the landing requirement, combined with the restriction to non-human consumption low value outlets, will encourage fishers to avoid unwanted catches by altering their fishing practices because there may be no economic gain in retaining small low-value fish. Improved selectivity of fishing gears remains a primary and important tool to avoid discards. Fishers have the potential to change the catches taken in their fishing operations and this will be an important approach to avoid negative business impacts of the discard ban.

The fishermen of the English NE Nephrops fishery initiated the study when they proposed a project, as part of the Cefas Fisheries Science Partnership Programme, to improve on a previously tested selective trawl design. The design under development is known as the Net Grid and the objective of the work was to further develop this design concept with the aim of producing a trawl that significantly reduces catches of unwanted fish without losing the target species of Nephrops. The Net Grid is comprised of a four panel box section inserted into a standard two-panel trawl into which an inclined sheet of netting is laced. On the top of the box section in front of the inclined sheet of netting is a fish escape hole. The netting acts as a physical barrier and guides fish out the escape-hole while Nephrops pass through the netting to the cod end.

The Net Grid was an industry driven alternative to the Swedish grid, and was originally tested within an ambitious timetable which achieved positive but limited results in 2012. The rigid construction of

Further Trials of the Net Grid Page 1

the Swedish grid design was considered inappropriate for vessels working in the English NE Nephrops fishery, due to handling difficulties with net drums and power blocks. One of the concerns from the fishermen after initial testing was that the Net Grid design, although highly effective at reducing cod catches, also indicated losses of Nephrops. Results from these earlier trials of the Net Grid were presented to STECF in 20121.

Further trials were conducted in 2013² where the overall objective was to develop a modified Nephrops trawl that delivered a catch weight for cod of no more than 5% of the total catch. It was agreed that the Net Grid concept was the most likely to achieve this. Following discussions with skippers and CEFAS staff, Seafish gear technologist Mike Montgomerie drew up netting plans for two versions of a modified Net Grid, both with an inclined sheet of netting of 200mm turned on the square and laced inside a four-panel section of the trawl. This mesh size was considered to be small enough reduce cod catches, but large enough to ensure no loss of Nephrops. These trials proved that Net Grid significantly reduces the catch of all fish, both marketable and discards and can be inserted into a standard Nephrops trawl without hindering the retention of Nephrops.

1.3 Objective

The aim of this project was to further develop the selective Net Grid trawl design to improve performance and enable skippers to better match their catch compositions to their quota allocations. The information from the trials will help skippers adapt to the Landing Obligation by avoiding unwanted fish in a fishery identified as having relatively high discard rates, and will demonstrate to managers the level of selectivity improvement that is currently achievable to help formulate Discard Plans.

A lot has been achieved with the development of the Net Grid so far. A trawl that enables the continuation of Nephrops catches when fish quotas are restricted is now available to the fleet. The previous project took the concept further by enabling the retention of marketable catches of groundfish whilst continuing to lose unwanted catches of whiting and haddock. This work aims to fine-tune this concept whilst also providing the flexibility so that marketable haddock and whiting can also be retained in a second cod end if desired.

The specific objective is to modify the incline panel and the escape section in the Net Grid to retain selected commercial species and size classes only but still minimise catches of other unwanted fish. This will be achieved by conducting field trials of a modified selective net and record the catch composition of escaping fish through a secondary cover two cod end and compare it with the commercial codend.

1 Trials of a Net Grid for the UK Nephrops trawl fisheries; Tom Catchpole, Frank Armstrong, Stuart Masson, Dave Price, Peter Clark, Steven Moss, Mark O’Brien, Kevin Duggan, Mike Manser, Ana Ribeiro Santos & John Hingley, Cefas Report; November 2012.²North East Coast Net Grid Trials; Frank Armstrong & Tom Catchpole, Cefas Report December 2013


2 Material and Methods

2.1 Vessel

Following an open tendering process, the fishing vessel LUC (SN 36) (Figure 1) was awarded a contract to undertake the survey work associated with this project over a period of 10 days. MFV LUC is a 17.8 m steel-hulled trawler based at North Shields, in the northeast of England and is skippered by Peter Clark.

Figure 1 LUC SN36, LOA 17.8 m, GT 69 t, 171 kw.

2.2 Gear

It is usual to conduct comparative trials on twin rig vessels or by parallel tows with two vessels, but this FSP was specifically for a single rig vessel so another solution had to be found. A 40 fathom (73m) footrope Nephrops trawl was constructed by Boris Nets. It contained a Net Grid section with a 200mm inclined panel and featured additional netting and an extra cod end to capture fish escaping from the trawl.

The Net Grid is comprised of a four panel box section inserted into a standard two-panel trawl into which an inclined sheet of netting is laced. On the top of the box section in front of the inclined sheet of netting is a fish escape hole. The netting acts as a physical barrier and guides fish out the escape-hole while Nephrops pass through the netting to the cod end. (Figure 2)


Figure 2 Standard Net Grid. (Illustration Mike Montgomerie Seafish)

For the experimental net a Net Grid section was inserted into a Boris trawl of the size and rig usually operated by the vessel (73m) with the exception that the SQMP was not inserted. This was to ensure that any effects observed would be solely attributable to the selectivity of the Net Grid. On the top sheet of the Net Grid level with the start of the incline panel on the bottom sheet, netting was attached and tapered side panels inserted, after the escape hole this continued for 50 meshes and then reverse tapered panels were fitted. Thus a four panel cover which returned to two panel netting was created. A cod end identical to the one of the main net was attached to the two panel netting after a reasonable length of sleeve had been created. Floats were attached to assist the netting to take shape. It was expected that this arrangement would demonstrate exactly which fish had exited the escape hole. When towing the original cod end would be nearest the seabed and the one capturing escaped fish would travel just ahead and above it. (See Figs 3-6 & 9).


Figure 3 Twin cod end arrangement.

Figure 4 Front view of netting cover.


Figure 5 Side view of netting cover.

Figure 6 Twin cod ends (Note that the left cod end will take a position above the right one when the net is operating.


2.3 Area and period of survey

2.3.1 Scoping Study

Because this was a non-standard net and methods of deploying and retrieving it needed to be examined, prior to the trials to test the alterations, it was necessary to spend four setting up the trawl, check it was fishing correctly and ensure a robust comparative test could be made.

On the 8th and 9th of October over six tows observations and methods were tried. The net proved easy deploy and after altering and adjusting the dog lines, retrieving both cod ends could be done effectively. It was decided that it was most convenient to empty the upper cod end into the hopper first and process this before then emptying the bottom cod end into the hopper. There were no fish of any type meshed other than in areas expected. The cover netting over the escape hole was particularly examined for meshed fish and none were found. This appeared to suggest that the method of attaching the upper cod end had been successful and was not hindering fish exiting the escape hole. From the first tow whiting (Merlangius merlangus) were more plentiful in the upper cod end and very few nephrops (Nephrops norvegicus) were found here. Other species of fish did not show any degree of separation (Figure 8).

Six more tows were completed on the 20th and 21st of October to examine effects of altering the incline panel to achieve better separation of fish. Initially the leading edge (bottom) of the incline panel was detached from the bottom sheet of the net and then 2 meshes per haul removed from it. After 8 meshes had been removed there was minimal increase in separation of fish observed. Slightly more flat fish were in the bottom cod end. Removing 1 mesh from the upper end of the incline panel resulted in the separation of whiting (Merlangius merlangus) being affected with more entering the bottom cod end. This mesh was then restated. Separation of nephrops (Nephrops norvegicus) was unaffected by these alterations to the incline panel.

With little observed positive difference in separation of species when altering the inclined panel, it was decided for the survey to alter the escape hole to try and achieve separation of fish by size and or species.

2.3.2 Survey

Twenty tows of 3-5 hours duration, i.e. typical of normal commercial practice, were conducted in the Farne Deeps fishing grounds off the North East coast of England. Towing speed was between 2.5 and 2.7 knots for all tows. The area of the main Nephrops fishing grounds within the Farne Deeps is classed as Functional Unit 6 (FU6) in the North Sea Nephrops stock assessment and is very small and highly localised. All fishing took place in the statistical rectangles 38E9 and 39E9 in ICES area IVb, bottom depths ranged between 46 and 81 m. (Figure 7)

One alteration of the Net Grid was operated for 10 tows from 4th till the 8 th of November for a total of 28hours 45minutes, another was operated for 10 tows between the 17th of November and the 3rd of December for a total of 37 hours 35 minutes.


Figure 7 Hauling positions, (Modification 1 red, Modification 2 blue) IVb (38E8, 39E8)(See Annex 3 for

shooting and hauling depths, times and exact positions.)

2.4 Experimental Design

Following discussions with the skipper, the experimental plan was agreed:

The aim of the experimental trials was to look at the effect of modifying the escape hole of the net grid after the scoping study. Two modifications were to be looked at during ten tows for each modification.

Trial 1: Modification one was to cover the escape hole with a section of T90 120mm netting, alon with removing 8 meshes from the bottom of the netting grid.

Trial 2: Modification two was to replace the top sheet of 80mm netting above the incline panel with T90 120mm netting including the area of the escape hole, along with removing 8 meshes from the bottom of the netting grid.

2.5 Sampling Plan

A fixed routine for handling and sorting the catch was maintained throughout the trials. Catches from the two cod ends and any fish trapped at the top of the grid were kept separate at all times. The net was drawn up to the vessel’s stern and the upper cod end was delivered into the vessel’s hopper and processed. The bottom cod-end was then delivered into the empty hopper and processed. The crew sorted the catch as they would normally; with the exception that all material usually discarded was retained in baskets for sampling as the “discard fraction”. Processed catch from each cod end and the trapped fish were kept separate till all quantities and details had been recorded.

Cefas observers sampled using standard techniques. For each haul all fish species caught were measured to the nearest cm below, the Nephrops carapace length was measured to the nearest mm below. All Cod caught were measured. Sub sampling was necessary for Nephrops and on occasions when the fish (other than Cod) catch was large, but sub samples reflected the total catch composition and raising factors were calculated. Length-weight relationships were applied to generate estimates of the catch weight of each species and therefore its weight in the total catch. For each of the main commercial species, the catches from the standard and Net Grid trawl were compared using a catch comparison statistical analysis method using the software SELNET which provides comparisons of fish catch at length by the two trawls through a continuous curve with a realistic confidence band. The analysis was applied to the catch data from all hauls considered valid (Annex 4).


Figure 8 Typical examples of the catch in the upper (top) and lower cod end (bottom)


Figure 9 Lower bag showing location of Net Grid and two cod ends.


3 Results

3.1 Catch composition

The total catch in the two trials was dominated mostly by whiting (WHG), with substantial catches of cod (COD), haddock (HAD), Nephrops (NEP), plaice(PLE) and dab (DAB). Catches of Nephrops were low in trial one, this was at the start of the Nephrops fishery season and Nephrops catches were not consistent at this time. Results from trial one are still considered valid because it was the selectivity towards fish that was the focus, and Trial 2 along with previous trials of the Net Grid gave confidence that selectivity towards Nephrops was unlikely to be effected by the modification tested in Trial 1.

Figure 10 overall catch compositions of the two trials, top 10 species by weight (kg)Table 1 Species codes, common names and scientific names for commercial species caught

SPECIES CODE Common Name Scientific NameMON ANGLERFISH (MONK) LOPHIUS PISCATORIUSBLL BRILL SCOPHTHALMUS RHOMBUSBLR BLONDE RAY RAJA BRACHYURACOD COD GADUS MORHUACUR CUCKOO RAY LEUCORAJA NAEVUSDAB DAB LIMANDA LIMANDAESB EUROPEAN SEABASS DICENTRARCHUS LABRAXHAD HADDOCK MELANOGRAMMUS AEGLEFINUSHAL HALIBUT HIPPOGLOSSUS HIPPOGLOSSUSHKE EUROPEAN HAKE MERLUCCIUS MERLUCCIUSHOM HORSE-MACKEREL (SCAD) TRACHURUS TRACHURUSJOD JOHN DORY ZEUS FABERLEM LEMON SOLE MICROSTOMUS KITTLIN COMMON LING MOLVA MOLVAMAC (EUROPEAN) MACKEREL SCOMBER SCOMBRUSNEP NORWAY LOBSTER NEPHROPS NORVEGICUSNSQ NORTHERN SQUID LOLIGO FORBESIPLA AMERICAN PLAICE (LR DAB) HIPPOGLOSSOIDES PLATESSOIDESPLE EUROPEAN PLAICE PLEURONECTES PLATESSASDR SPOTTED RAY RAJA MONTAGUISOL SOLE (DOVER SOLE) SOLEA SOLEA (=S.VULGARIS)THR THORNBACK RAY (ROKER) RAJA CLAVATATUB TUB GURNARD TRIGLA (CHELIDONICHTHYS) LUCERNATUR TURBOT SCOPHTHALMUS MAXIMUS (=PSETTA MAXIMA)WHG WHITING MERLANGIUS MERLANGUS


WIT WITCH GLYPTOCEPHALUS CYNOGLOSSUS3.2 Percentage of catches separated between the cod end and cover

A similar result was seen with both modifications (Figure 11), with the same species moving through into the top cover cod end. The majority of catches of mackerel (MAC), whiting (WHG), haddock (HAD), horse mackerel (HOM) and in Trial 2 bass (ESB) and northern squid (NSQ), were taken in the top cover cod end having passed through the escape section ahead of the inside netting grid, indicating that these species utilise escape opportunities in the top of the trawl and these fish were small enough to pass through the large mesh T90 sections that replace the escape opening. 70% of whiting and 58-75% of haddock were caught in the top cod end and therefore would have avoided capture with these designs.

Flat fish species, including plaice, lemon sole, sole, dab and brill were caught in the bottom cod end along with species of ray. Cod were mostly caught in the bottom cod end (70-85%) and therefore would be mostly retained with a commercial application if this design.

BLL CURHAL LIN MON

NEP THR

TUR

LEM DABSO

LPLE PLA SD

RTU

BCOD

MURJO

DHKE

HOMWHG

HADMAC

0%10%20%30%40%50%60%70%80%90%

100%

Trial 1 percentage of total catch weight in top and bottom codends

Bottom Top


BLL BLR CURHAL

JOD

MONSD

RTH

RTU

RNEP WIT SO

LLEM PLE DAB

COD PLA TUB

HKEMUR LINMAC

HOMHAD

WHGNSQ ESB

0%

10%20%

30%

40%50%

60%70%

80%

90%

100%

Trial 2 percentage of total catch weight in top and bottom codends

Bottom TopFigure 11 Percentage of catches separated between the cod end and cover Trial 1 and Trial 2


3.3 Trial 1 retained and discarded in bottom (commercial) cod end

In Trial 1, with the T90 section replacing the open escape section, fish passing into the bottom (commercial) cod end represent those fish that would have been retained in the trawl. Therefore, most of the haddock, cuckoo ray, spotted ray and thornback ray, that would have been retained trawl would have been discarded (Figure 12). Just under half of the plaice, whiting and lemon sole that were caught in the bottom cod end were discarded. Most or all of the other species caught in the bottom cod end would have been retained. It is important to note that the discard patterns seen here may not reflect the desired catch composition when subject to the landing obligation and also the catch numbers of many of these species was low. The data does show that the design enables a proportion of the commercial catches of fish to be retained with this Net Grid trawl design, where previous variants excluded almost all of the fish, but some unwanted fish are also retained.

BLL HALHOM JO

D LIN MACMUR

NEP SOL

TUB

TUR

MONCOD PLA DAB

WIT HKELEM WHG PLE TH

RSD

RCUR

HAD0%

20%

40%

60%

80%

100%

Trial 1 percentage retained and discarded weights in bottom codend

Retained DiscardFigure 12 Trial 1 retained and discarded in bottom (commercial) cod end

3.4 Trial 1 retained and discarded in top (cover) cod end

In Trial 1, fish passing into the top (cover) cod end represent those fish that would have escaped the trawl. Therefore, most of the haddock, spotted ray, lemon sole, and whiting that would have escaped the trawl would have been discarded if caught. Just under half of the plaice, caught in the top cod end would have been discarded. Most or all of the other species caught in the top cod end would have been retained, including cod, sole and hake. Again, it is important to note that the discard patterns here may not reflect the desired catch composition when subject to the landing obligation and also the catch numbers were low. The data does show that some marketable catches of fish would be lost with this design.

DAB HKE HOM JOD MAC MUR SOL TUB WIT COD PLE PLA WHG LEM HAD SDR0%

10%20%30%40%50%60%70%80%90%

100%

Trial 1 percentage of retained and discarded weights in top codend

Retained Discard Figure 13 Trial 1 retained and discarded in top (cover) cod end


3.5 Trial 2 retained and discarded in bottom (commercial) cod end

In Trial 2, with the T90 section behind the netting grid and the escape section covered, fish passing into the bottom (commercial) cod end represent those fish that would have been retained in the trawl. Therefore, most of the cuckoo ray and spotted ray that would have been retained (Figure 12). Around half of the plaice, whiting, lemon sole and haddock caught in the bottom cod end were discarded. Most or all of the other species caught in the bottom cod end would have been retained. It is important to note that the discard patterns seen here may not reflect the desired catch composition when subject to the landing obligation and also the catch numbers of many of these species was low. The data does show that the design enables a proportion of the commercial catches of fish to be retained with this Net Grid trawl design, where previous variants excluded almost all of the fish, but some unwanted fish are also retained.

BLL BLR HALJO

D LIN MACMON

NSQ SOL

TUR

NEPHOM TU

BHKE

MURWIT

DABCOD

THR

PLA HAD PLEWHG

LEM CURSD

R0%

20%

40%

60%

80%

100%

Trial 2 percentage of retained and discarded weights in bottom codend

Retained DiscardFigure 14 Trial 2 retained and discarded in bottom (commercial) cod end

3.6 Trial 2 retained and discarded in top (cover) cod end

In Trial 2, fish passing into the top (cover) cod end represent those fish that would have escaped the trawl. Therefore, most of the plaice, cod, and whiting that would have escaped the trawl would have been discarded if caught. Around half of the dab, long-rough dab, ling and, and haddock caught in the bottom cod end were discarded. Most or all of the other species caught in the top cod end would have been retained, including cod, sole and hake. Again, it is important to note that the discard patterns here may not reflect the desired catch composition when subject to the landing obligation and also the catch numbers were low. The data does show that some marketable catches of fish would be lost with this design.

ESB HKE HOM LEM MAC NEP NSQ SOL TUB WIT MUR HAD LIN PLA DAB WHG COD PLE0%

10%20%30%40%50%60%70%80%90%

100%

Trial 2 percentage of retained and discarded weights in top codend

Retained DiscardFigure 14 Trial 2 retained and discarded in top (cover) cod end


3.7 Trial 1 effect of modifications on length of fish caught

The length frequencies for the main species of the fish caught in the two cod ends in Trial 1 are shown in Figure 15. These indicate that much more of the whiting and haddock were caught in the top (cover) cod end; i.e. they would have escaped the trawl. The statistical analysis shows that for whiting the were significantly more whiting in the top cod end across the length range whereby the smaller the fish the more likely they were to swim through the T90 panel and be caught in the top cover cod end (Figure 16). For haddock, again more fish across the length range were caught in the top cod end, but here we see that the larger fish were more likely to be caught in the top cod end.For cod, significantly more fish were caught in the bottom cod end, but a substantial proportion were caught in the top; and there was no effect of length. For dab, plaice and Nephrops, almost all catches were taken in the bottom codend.

Figure 15 Length frequency plots for main species (numbers at length (cm); red top (cover) cod end; black bottom (commercial) cod end. Length is total length for fish and carapace length for Nephrops.


Figure 16. Results from the SELNET catch comparison analysis. Interpretation: a value of 0.5 indicates an equal split between the top (cover) cod end and the bottom (commercial) codend. Cross points are pooled experimental proportions and the bold lines around the modelled curve (dotted lines) represent the 95% confidence regions. The length frequency from the standard trawl is given (grey shading) to provide context of the result. Therefore, when the modelled dotted line is above the 0.5 level more at this length were retained in the top (cover) cod end and would have escaped the trawl.


3.8 Trial 2 effect of modifications on length of fish caught

The length frequencies for the main species of the fish caught in the two cod ends in Trial 2 are shown in Figure 17. These indicate that much more of the whiting and haddock were caught in the top (cover) cod end; i.e. they would have escaped the trawl. The statistical analysis shows that for whiting the were significantly more whiting in the top cod end across the length range whereby the smaller the fish the more likely they were to swim through the T90 panel and be caught in the top cover cod end (Figure 18). For haddock, again more fish across the length range were caught in the top cod end, but here we see that the larger fish were more likely to be caught in the top cod end.For cod, significantly more fish were caught in the bottom cod end, but a proportion were caught in the top; and the smallest cod were more likely to be caught in the top cod end. For dab, plaice and Nephrops, almost all catches were taken in the bottom codend.

Figure 17 Length frequency plots for main species (numbers at length (cm); red top (cover) cod end; black bottom (commercial) cod end. Length is total length for fish and carapace length for Nephrops.


Figure 18. Results from the SELNET catch comparison analysis. Interpretation: a value of 0.5 indicates an equal split between the top (cover) cod end and the bottom (commercial) codend. Cross points are pooled experimental proportions and the bold lines around the modelled curve (dotted lines) represent the 95% confidence regions. The length frequency from the standard trawl is given (grey shading) to provide context of the result. Therefore, when the modelled dotted line is above the 0.5 level more att this length were retained in the top (cover) cod end and would have escaped the trawl.


4 Discussion

The specific objective of this study was met, to modify the incline panel and the escape section in the Net Grid trawl to retain selected commercial species and size classes only but still minimise catches of other unwanted fish.

Following some preliminary trials two modifications were selected for trialling. The Net Grid was originally designed to reduce catches of cod to less than 1.5% of the catch, to meet the criteria of a highly selective gear and so be exempt from fishing effort restrictions. To achieve this, a selection grid was chosen, as it has been demonstrated that some form of physical selection process is required to separate cod from Nephrops, which behave in a similar way when inside the trawl during the capture process. Prior to this project the development of the Net Grid, by Cefas and a number of skippers from the NE English Nephrops fishery, had reached a stage at which it was possible to catch Nephrops with very low cod catches, however, this also meant large reductions in the catches of other marketable fish. At this time, the Net Grid demonstrated significant reductions in landings of fish of 85% less whiting, 74% less haddock, 90% less plaice and 66% less lemon sole by weight.

Therefore, while the Net Grid was efficient at minimising fish catches while retaining Nephrops, it was considered a rather blunt tool, whereby skippers could either catch fish (including unwanted fish) and Nephrops with a conventional trawl or only Nephrops with the Net Grid trawl. The idea came from the industry to fine tune the Net Grid design so that it could retain some of the marketable fish while still avoiding the unwanted catches. During this time also, the policy emphasis shifted from one focussed on the cod recovery plan to one on implementing the landing obligation under the reformed CFP. And with this came a shift of emphasis onto the species which pose the greatest economic risk to the fleet with the introduction of the discard ban, which in this fishery is primarily whiting.

The modifications selected were therefore designed to reduce the escapement of marketable and valuable fish, while still allowing unwanted fish to escape. This meant the modification of the escape hole at the top of the inclined netting grid and reducing the length of the inclined netting grid to that there was space at the bottom of the grid under which fish could pass. Two modifications were tested, a simple covering of the escape hole with T90 120mm netting and the insertion of a larger section of T90 120mm netting, above the netting grid in the top of the trawl including the area of the escape hole. Both designs also included removing 8 meshes from the bottom edge of the netting grid.

To test the two designs, it was necessary to record the fish that escaped through the T90 sections ahead of the netting grid and compare with what was caught in the cod end. This was done by designing a cover over the escape sections which terminated in a top (cover) cod end. The catches retained in the two cod ends demonstrated which fish had entered the trawl and escaped through the T90 sections compared with those which has been retained in the trawl and would have been caught by this design if used commercially.

In both trials, whiting, mackerel, haddock, horse mackerel were mostly caught in the top cod end. These species are known to move to the top of the trawl during the capture process and were small enough to pass through the 120mm meshes of the T90 sections. Flat fish species, including plaice, lemon sole, sole, dab and brill were predominantly caught in the bottom cod end along with species of ray. Other demersal species were split between the top and bottom cod ends including cod and gurnards. These fish will have either not attempted to escape from through the T90 sections or have been too large to pass through the 120mm T90 meshes and either passed through or under the netting grid. In trial 1, there was a 30:70 split for whiting between the top and bottom cod ends, 70:30 split for cod and 25:75 split for haddock. In trial 2, the equivalent figures were 27:73 for whiting, 86:14 for cod and 42:58 for haddock. The reason for the reduced level of separation for haddock in trial 2 is not understood.

For whiting, analysis showed that the smaller fish were most likely to escape through the T90 sections, and for haddock the opposite was true. The reasons for this are unclear, although this may relate to the relative swimming strength of different sizes/ages of fish and the behavioural positioning of different sized fish inside


the trawl. However, with the significant proportion of these species passing to the top cod end shows that the modifications made enabled most of the fish of species that pose the highest risk under the landing obligation to escape while retaining a substantial proportion of the marketable catches.

5 Conclusions

These modifications to the Net Grid trawl show it is possible to maintain catches of flatfish, rays and most cod, while avoiding most haddock and whiting and other unwanted catches. Whiting has been identified as the species posing the highest risk to fishing businesses in the transition to the discard ban in this fishery so there is useful application for this design. These latest variants of the Net Grid, while retaining marketable catches also retain more unwanted catches that previous versions, also, earlier variants which avoid almost all marketable catches are the only design currently available to avoid cod while targeting Nephrops. However, these designs provide more options to skippers who are motivated to change the selectivity of their trawls so that their catches composition matches more closely with quota composition and so assist them in the transition to the landing obligation.


6 References

Catchpole, T.L., Revill, A.S., Dunlin, G., 2006. An assessment of the Swedish grid and square mesh cod end in the English (Farne Deeps) Nephrops fishery. Fisheries Research, 81, 118-125.

Trials of a Net Grid for the UK Nephrops trawl fisheries; Tom Catchpole, Frank Armstrong, Stuart Masson, Dave Price, Peter Clark, Steven Moss, Mark O’Brien, Kevin Duggan, Mike Manser, Ana Ribeiro Santos & John Hingley, Cefas Report; November 2012.

7 Acknowledgements

Peter Clark and the crew of the LUC are warmly thanked for their co-operation throughout the project; they were a pleasure to work with.

John Howard and his staff at Boris are thanked for constructing the twin cod end net. Their construction of an innovative net which fished with few problems greatly assisted the project. Input from numerous fishers before the fishing trials is gratefully acknowledged, as is the assistance and support provided by the FSP team (Mike Fox and Sarah Walmsley) within Cefas.

Defra are also thanked for supporting this project.


8 Annexes

8.1 Annex 1 Detailed Operations Plan

THE CENTRE FOR ENVIRONMENT, FISHERIES AND AQUACULTURE SCIENCE(Lowestoft Laboratory, Suffolk, NR33 0HT, England)

This document describes the agreements reached by all parties at a planning meeting held in North Shields, 07/09/2015.

Detailed Operations PlanFISHERIES SCIENCE PARTNERSHIP – Ref 2015-16(47) Further Trials of the Net Grid in the English

North East Nephrops Single Rig Trawl Fishery

Vessel: LUC SN36 Skipper: Peter ClarkProject Manager: Frank Armstrong

Aim: The specific aim is to modify the escape section at the top of the trawl in front of the selection grid

(Net Grid) to retain some species but still minimise catches of others to help skippers adapt to the

Landing Obligation by avoiding unwanted fish, in a fishery identified as having relatively high discard

rates.

Fishing gear: 40 fathom Boris Nephrops trawl containing Net Grid section with 200mm inclined panel and

extra cod end to capture fish escaping from the trawl.

Area and period of operation: The work will take place during September and October 2015 The vessel will sail from and return to North Shields. The trials will be conducted in ICES Area IVb and it is expected that most of the fishing will

take place in statistical rectangles 38E8 or 39E8

Fishing activities: The skipper has the experience of fishing and the grounds and should advise where the trials

should take place. The fishing programme should be agreed by the skipper and the project manager. The fishing should be representative of normal commercial practice as closely as possible

with the focus on Nephrops as the target species. The number of tows may be reduced on a given day as dictated by sea condition, volume of

catch, gear damage, as agreed by the skipper and the project manager. If days at sea are lost due to adverse weather conditions and/or mechanical failure then they

should be rescheduled for completion at the earliest opportunity. Discarded species will be retained in baskets to ensure the accuracy of quantities before

discarding. The component of the catch from the main cod end, the additional cod end over


the Net Grid escape hole and the fish retained between the inclined panel and the Net Grid escape hole cover must be kept separate

If the vessel encounters large catches there may be a requirement for the vessel to suspend deploying the gear until the previous haul has been processed, in order to keep the catch from each haul separate.

The conditions and details of the ITT, contract and dispensation will be upheld.

Legalities and quota: Fishing will be “off quota”. All tows carried out under the charter will be for testing the

experimental gear; no other fishing will take place on these days. Undersized fish can be retained on board for measuring but must not be landed. The relevant dispensation will be issued by the MMO and will be carried on board the vessel

for the duration of the trials. It will be made available to any Marine Enforcement Officer on request.

The dispensation will only be valid if the terms of the issued document are met. For E- logbook completion the reason for sailing (anticipated activity in some e-logs) given in

the Departure (DEP) message must be “SCR” (Scientific Research) and not “FSH” (Fishing). This identifies the trip as one subject to Quota dispensation.

Sorting and recording the catch: The entire catch must be made available for sampling. The crew will be required to assist in sorting the catch and will prepare it for sale.

Data to be recorded by the skipper: Date Tow number Shooting and hauling times and shooting and hauling position (latitude and longitude to the

nearest minute) Shooting and hauling depth Average speed over the ground Time and position of any significant change in tow direction Log sheets for recording this information will be provided by the project manager at the

start of the trials. The skipper should maintain a diary of activities not recorded in any of the above, including,

for each tow, a description of the Net Grid arrangement, the large mesh cover over the Net Grid escape hole, and the additional cod end fitted to collect fish escaping through the large-mesh cover over the Net Grid escape hole.

Data to be recorded by Cefas observers: Observers will record length frequencies of all retained and discarded fish

species ,separately for the main cod end of the net, the catch retained between the incline panel and the covered Net Grid escape hole, as well as in the additional cod end fitted over the Net Grid escape hole.

All hauls will be sampled during the trials. Where catch quantities are high observers will sub-sample and record accurate raising

factors. The observer will maintain a diary of activities, to produce a draft cruise report for

submission to Cefas immediately after the cruise. The cruise narrative will be written at sea


and read, agreed and signed by the skipper (the report will bear the sentence “seen in draft by skipper”).

Safety: Safety takes priority over all other aspects of the charter. The skipper has ultimate authority on board and is responsible for ensuring the safety of the

vessel and all parties on board. The attached “Working hours and safety at sea” document sets out the provisions and

requirements for Cefas observers.

Provision of sales notes: A copy of the landings/sales notes is required by Cefas to enable 95% of the total agreed

price (including VAT) to be paid and should be provided to the project manager.

Contacts: It is the responsibility of the project manager to contact the local MMO office (and IFCA

office if necessary) to advise the start and end of the trials prior to departure, and also to notify the Cefas shore based contact on sailing and landing.


8.2 Annex 2 Detailed Net Plans


8.3 Annexe 3 Shooting and hauling times, depths and positions

3.1 Modification 1

HAUL Shot Date Time

Depth

(m.)

Lat. Deg

Lat. Min

Lon.

Deg

Lon.

Min Haul Date Time

Depth

(m.)

Lat. Deg

Lat. Min

Lon.

Deg

Lon.

Min

Tow Duration (mins)

104/11/201

506:4

5 51 55 2 -1 -1504/11/201

510:3

0 81 54 57 0 -58 225

204/11/201

512:0

0 60 54 55 -1 -404/11/201

515:0

0 49 54 59 -1 -12 180

305/11/201

506:4

0 46 54 57 -1 -1305/11/201

509:4

5 57 54 55 -1 -7 185

405/11/201

510:3

0 57 54 55 -1 -805/11/201

513:0

0 77 55 0 -1 -8 150

506/11/201

507:0

0 60 55 0 -1 -906/11/201

509:4

5 75 54 55 -1 -2 165

606/11/201

510:3

5 75 54 55 -1 -206/11/201

513:3

0 62 55 0 -1 -11 175

707/11/201

506:5

5 59 55 1 -1 -1007/11/201

510:0

0 77 54 54 -1 -1 185

807/11/201

510:4

0 77 54 54 -1 -107/11/201

513:3

5 70 55 0 -1 -8 175

908/11/201

507:0

0 55 54 59 -1 -1008/11/201

509:1

5 79 54 56 -1 -1 135

1008/11/201

510:0

0 77 54 57 0 3908/11/201

512:3

0 55 54 57 -1 -8 150

3.1 Modification 2

HAUL Shot Date Time

Depth

(m.)

Lat. Deg

Lat. Min

Lon.

Deg

Lon.

Min Haul Date Time

Depth

(m.)

Lat. Deg

Lat. Min

Lon.

Deg

Lon.

Min

Tow Duration (mins)

117/11/201

507:0

0 51 55 3 -1 -1804/11/201

511:0

0 51 55 3 -1 -16 240

217/11/201

511:5

0 51 55 3 -1 -1604/11/201

515:1

5 49 55 4 -1 -17 205

330/11/201

507:1

5 49 54 58 -1 -1205/11/201

510:3

0 51 54 51 -1 -6 195

430/11/201

511:1

5 49 54 51 -1 -605/11/201

515:0

0 55 55 0 -1 -12 225

501/12/201

507:1

0 49 54 58 -1 -606/11/201

511:0

0 53 54 50 -1 -5 230

601/12/201

511:4

5 53 54 50 -1 -506/11/201

515:1

0 51 55 0 -1 -13 205

702/12/201

507:3

0 49 54 57 -1 -1307/11/201

511:1

5 46 54 48 -1 -5 225

8 02/12/201 12:0 46 54 48 -1 -5 07/11/201 16:0 46 54 56 -1 -13 240


5 0 5 0

903/12/201

507:0

0 46 54 56 -1 -1308/11/201

511:1

0 46 54 53 -1 -12 250

1003/12/201

512:0

0 46 54 53 -1 -1208/11/201

516:0

0 46 54 57 -1 -13 240


8.4 Annex 5 Skipper’s comments

Net grid trial aboard LUC SN36 2015

We started off the trial with 4 days to get happy with the gear and to make any adjustments. First impression of the two cod end set up is it would never work or would be a load of trouble! But I was wrong.There was an encouraging sign of prawns the 1st day, which then took off. We were separating the fish right from the start. We started to cut away the bottom of the grid so as to try and let turbots, monks, flats etc pass under the grid into the bottom cod end rather than go into the escape one, which worked with medium success.When we covered the escape hole with the larger square mesh we did keep more fish in the bottom cod end but had a big problem with fish jamming up the top of the grid, up to a box of mixed fish at times, which had to be cut out of the net, in fine weather this was a pain at best in poorer weather it was dangerous. We did try cutting letterbox holes in the top of the grid for this fish to pass clear but it was letting a large amount of whiting through so we mended this back up.

There were a lot of codlings and whiting at the start of the trial and a good mix of other fish but very little prawns, but we still had success splitting the whiting from the rest of the shot while keeping a larger selection of mixed fish which would have been lost with the escape hole open.The biggest bulk we took was further east in deeper water, a lot of small haddocks. The bulk was split evenly between both cod ends. I think this happened because the top cod end filled putting weight on the top sheet closing the netting over the escape square mesh.

One problem which would of happened had we been fishing commercially and not on a trial would be my catch composition would have been wrong, the amount of whiting we were losing and the amount of cod there was I would have to had to dump cod to comply with the percentages aloud by this stupid rule. We were solving one problem getting rid of juvenile whiting but creating discards of cod because of catch composition rules! THESE RULES CANNOT WORK UNDER A DISCARD BAN IN MY OPINION.

2nd part of the trial with the smaller square mesh escape hole. Codlings had taken off but there was still a good mix of other fish and a better sign of prawns. We still had a problem with fish getting jammed at the top of the grid. This seemed to be working well at separating whiting and haddocks, this was my preferred square mesh size but think we could of went down in size again with the same results of letting the juveniles escape but keeping a larger percentage of sized fish which I have quota to catch and which were making good money on the market. The last day was are best day for prawns and we seemed to be competing with the other boats around us, so am fairly confident the gear was working and would be happy to work it, although I would still have liked to see a camera or flume tank tests carried out just to see how everything is performing. It made the work easier having the prawns split from the fish and a quicker sort, the quality of the whiting was 1st class not being mixed in with the prawns.

I believe there is still a few improvements to be made which I have ideas for solving and believe the results we have getting justify taking them further and I will be putting forward another FSP in the future. If a camera became available. I would be happy to put the net back aboard for a few days free of charge to see if there was any problems that need addressing with this arrangement before hopefully another FSP was accepted with my ideas for improvement and put out to tender.

Peter ClarkSkipper LUC SN36

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Documents

Introduction - Seafish · Web viewTo test the two designs, it was necessary to observe the fish that escaped through the T90 sections and compare with the fish that were retained